Mercutio is one of the cleverest, wittiest characters in all of Shakespeare's tragedies. He is constantly poking fun at Romeo's lovelorn melancholy, using bawdy sexual double entendres and puns that would have delighted Shakespeare's audiences. When Romeo is hiding in the Capulet's garden, for example, Mercutio tries to goad him into revealing himself through sexual references to Rosaline, the former object of his longing:

I conjure thee by Rosaline's bright eyes. By her high forehead and her scarlet lip, By her fine foot, straight leg, and quivering thigh, And the demesnes that there adjacent lie, That in thy likeness thou appear to us!

Later, in a long and comical speech on love, he mockingly describes love in explicitly sexual terms:

...For this drivelling love is like a great natural that runs lolling up and down to hide his bauble in a hole.

Later in one his more famous scenes, he relentlessly mocks the Nurse by comparing her dress to a sail (suggesting she is massively overweight) and begging her servant Peter to give the Nurse a fan to hide her face. Mercutio, then, is a foil for Romeo, who is always moaning about love, and he serves as a consistent source of comic relief throughout the play. A notable exception is his death scene, when he recklessly provokes a duel with Tybalt, and in his poignant speech blaming the Montagues and Capulets for his death.